Different types of wireless mobile communication devices such as mobile telephone handsets, laptop and tablet computers, USB adaptors and other electrically small radio platforms are available. Such devices are intended to be compact and therefore are easily carried on one's person.
There exists a need to increase system capacity while still maintaining compact devices. One method for improving signal quality and data transmission rates is MIMO (multiple-input and multiple-output). MIMO is the use of multiple antennas at both the transmitter and receiver to improve data capacity and performance for communication systems without additional bandwidth or increased transmit power. Similarly, antenna diversity (often just at the receiving end of a radio link) improves signal quality by switching between two or more antennas, or by optimally combining the signals of multiple antennas.
However, antennas in close proximity to each other are prone to performance degradation due to electromagnetic interference. Therefore, it is desirable to develop devices designed to isolate the antennas and minimize any performance degradation.
For effective operation, both MIMO and diversity techniques require a degree of isolation between adjacent antennas that is greater than is normally available when the antennas are disposed electrically close to one another, as on a typical portable device.
CN201289902 (Cybertan) describes a structure in which two antennas are disposed such that one antenna is arranged each side of a grounding surface and connected with the grounding surface through a feed-in point. The isolation between the antennas is improved by perforating the grounding surface with an isolating slotted hole between the first antenna and the second antenna. CN201289902 does not however disclose the arrangement of a slot or notch in the edge of the grounding surface, or the tuning of such a notch.
GB2401994 (Antenova) discloses how the isolation between two similar antennas may be improved by forming at least one slot, cut, notch or discontinuity in the edge of a conductive ground plane in a region between the feed lines of the two antennas.
U.S. Pat. No. 6,624,789 (Nokia) discloses that the isolation is improved if the length of the cut is substantially equal to one quarter-wavelength of the operating frequency band.
EP2387101 (Research In Motion) further discloses how a slot in a conductive ground plane may be meandered or bifurcated.
None of these patents describe the tuning of a slot or notch although U.S. Pat. No. 6,624,789 does show how placing a switch across the slot may be used to change the effective slot length.
All of the references identified above are hereby incorporated into the present application by way of reference, and are thus to be considered as part of the present disclosure.